This invention relates generally to pin retractors for semi-trailers also referred to as semi-trailer tandems, and more specifically to a relatively simple mechanism for retracting multiple pins of a tandem using an air spring.
Conventional semi-trailers of the type hauled over the road by trucks connect to the truck at a hitch or fifth wheel, and include a tandem, referring to a pair or multiple pairs of parallel axles. In many trailers, the tandem is slidable forward and backward relative to the trailer for adjusting the load on the rear axle or axles. The ability to move the tandem relative to the cargo containing portion of the semi-trailer is desirable for a number of reasons. When a tractor and semi-trailer must maneuver around city streets, relatively tight corners are common. By moving the tandem forward, it is easier to negotiate tight corners. In contrast, when traveling on highways, moving the tandem to the rear of the cargo container puts a larger percentage of the load on the axles of the tractor, providing a better ride.
The tandem is secured in position relative to the trailer using at least one and preferably four retractable lock pins. The pins are typically provided in pairs, members of each pair engaging opposing points of left and right rails on the trailers. Being biased, usually by a coiled spring or the like, the pins extend laterally or transversely to the direction of travel of the trailer and engage openings in the depending rails having a linear array of the openings for accommodating various trailer/slider positions. Using the pins, the slider is held in position relative to the trailer.
When the pins are retracted, they are also disengaged from the openings or apertures in the trailer rails, and allow the trailer to be slid forward or backwards relative to the slider. It is conventional to provide a front and/or rear stop for preventing excessive travel of the trailer relative to the slider to the extent that the slider disengages from the trailer.
While manual mechanisms are well known for retracting the lock pins, they are subject to jamming, and are inherently more labor intensive for the operator. Pneumatically powered pin retraction mechanisms have been developed, but are considered costlier and mechanically more complicated than the manual systems. In the latter systems, a shaft rotates under the power of a pneumatic inflatable member, which retracts the pins. Air is supplied to the pneumatic pin retraction system from the existing vehicle trailer braking system. Conventional pneumatic pin retraction systems are considered more prone to breakdown and require relatively more maintenance than manual systems.
Thus, there is a need for an improved automatic slider locking pin system that addresses the above-identified drawbacks.